Mathematical Models of Proprioceptors. I. Control and Transduction in the Muscle Spindle

2006 ◽  
Vol 96 (4) ◽  
pp. 1772-1788 ◽  
Author(s):  
Milana P. Mileusnic ◽  
Ian E. Brown ◽  
Ning Lan ◽  
Gerald E. Loeb
Keyword(s):  
Muscle Spindle ◽  
Motor Behavior ◽  
Realistic Model ◽  
Medial Gastrocnemius ◽  
Parameter Determination ◽  
Model Parameters ◽  
Data Sets ◽  
Temporal Properties ◽  
Single Set

We constructed a physiologically realistic model of a lower-limb, mammalian muscle spindle composed of mathematical elements closely related to the anatomical components found in the biological spindle. The spindle model incorporates three nonlinear intrafusal fiber models (bag1, bag2, and chain) that contribute variously to action potential generation of primary and secondary afferents. A single set of model parameters was optimized on a number of data sets collected from feline soleus muscle, accounting accurately for afferent activity during a variety of ramp, triangular, and sinusoidal stretches. We also incorporated the different temporal properties of fusimotor activation as observed in the twitchlike chain fibers versus the toniclike bag fibers. The model captures the spindle's behavior both in the absence of fusimotor stimulation and during activation of static or dynamic fusimotor efferents. In the case of simultaneous static and dynamic fusimotor efferent stimulation, we demonstrated the importance of including the experimentally observed effect of partial occlusion. The model was validated against data that originated from the cat's medial gastrocnemius muscle and were different from the data used for the parameter determination purposes. The validation record included recently published experiments in which fusimotor efferent and spindle afferent activities were recorded simultaneously during decerebrate locomotion in the cat. This model will be useful in understanding the role of the muscle spindle and its fusimotor control during both natural and pathological motor behavior.

scholarly journals Memory patterns for choice adaptation in dynamic environments

2020 ◽  
Author(s):  
Emmanouil Konstantinidis ◽  
Jason L. Harman ◽  
Cleotilde Gonzalez
Keyword(s):  
Computational Models ◽  
Future Research ◽  
Model Parameters ◽  
Data Sets ◽  
Individual Memory ◽  
Learning And Adaptation ◽  
Decision Environments ◽  
Optimal Adaptation ◽  
Over Time

An important aspect of making good decisions is the ability to adapt to changes in the values of available options. Research suggests that we are poor at changing behavior and adapting our choices successfully. This work contributes to clarifying the role of memory on learning and successful adaptation to changing decision environments. We test the effects of the direction of change and the type of feedback using a decisions from experience binary choice task, where individuals learn the outcomes and their associated probabilities from feedback received after selecting between available choice options. The results revealed a robust effect of the direction of change: risk that becomes more rewarding over time is harder to detect than risk that becomes less rewarding over time; and even with full information about the outcomes of choice options people showed sub-optimal adaptation to change. We rely on three distinct computational models to interpret the role of memory on learning and adaptation. The distributions of individual model parameters were analyzed in relation to participants' ability to successfully adapt to the changing conditions of the various decision environments. Consistent across the three models and two distinct data sets (our experimental data and other researchers' data), results revealed the value of recency as an individual memory component for choice adaptation. Individuals relying more on recent experiences were more successful at adapting to change, regardless of the direction of change. We explain the value and limitations of these findings as well as opportunities for future research.

Participant recruitment and data collection through Facebook: the role of personality factors

2017 ◽  
Author(s):  
Sean Chandler Rife ◽  
Kelly L. Cate ◽  
Michal Kosinski ◽  
David Stillwell
Keyword(s):  
Data Collection ◽  
Social Research ◽  
Personality Factors ◽  
The Internet ◽  
Data Sets ◽  
Social Networking Service ◽  
Participant Recruitment ◽  
Conducting Research ◽  
Promising Avenue

As participant recruitment and data collection over the Internet have become more common, numerous observers have expressed concern regarding the validity of research conducted in this fashion. One growing method of conducting research over the Internet involves recruiting participants and administering questionnaires over Facebook, the world’s largest social networking service. If Facebook is to be considered a viable platform for social research, it is necessary to demonstrate that Facebook users are sufficiently heterogeneous and that research conducted through Facebook is likely to produce results that can be generalized to a larger population. The present study examines these questions by comparing demographic and personality data collected over Facebook with data collected through a standalone website, and data collected from college undergraduates at two universities. Results indicate that statistically significant differences exist between Facebook data and the comparison data-sets, but since 80% of analyses exhibited partial η2 < .05, such differences are small or practically nonsignificant in magnitude. We conclude that Facebook is a viable research platform, and that recruiting Facebook users for research purposes is a promising avenue that offers numerous advantages over traditional samples.

Parameter Determination for Chloride and Tritium Transport in Undisturbed Lysimeters during Steady Flow

1992 ◽  
Vol 23 (2) ◽  
pp. 89-104 ◽  
Author(s):  
Ole H. Jacobsen ◽  
Feike J. Leij ◽  
Martinus Th. van Genuchten
Keyword(s):  
Experimental Data ◽  
Unsaturated Flow ◽  
Transport Model ◽  
Time Moment ◽  
Breakthrough Curves ◽  
Coarse Sand ◽  
Retardation Factor ◽  
Parameter Determination ◽  
Model Parameters ◽  
Water Fraction

Breakthrough curves of Cl and 3H2O were obtained during steady unsaturated flow in five lysimeters containing an undisturbed coarse sand (Orthic Haplohumod). The experimental data were analyzed in terms of the classical two-parameter convection-dispersion equation and a four-parameter two-region type physical nonequilibrium solute transport model. Model parameters were obtained by both curve fitting and time moment analysis. The four-parameter model provided a much better fit to the data for three soil columns, but performed only slightly better for the two remaining columns. The retardation factor for Cl was about 10 % less than for 3H2O, indicating some anion exclusion. For the four-parameter model the average immobile water fraction was 0.14 and the Peclet numbers of the mobile region varied between 50 and 200. Time moments analysis proved to be a useful tool for quantifying the break through curve (BTC) although the moments were found to be sensitive to experimental scattering in the measured data at larger times. Also, fitted parameters described the experimental data better than moment generated parameter values.

scholarly journals Theory and Applications of the Unit Gamma/Gompertz Distribution

Mathematics ◽  
2021 ◽  
Vol 9 (16) ◽  
pp. 1850
Author(s):  
Rashad A. R. Bantan ◽  
Farrukh Jamal ◽  
Christophe Chesneau ◽  
Mohammed Elgarhy
Keyword(s):  
Stochastic Ordering ◽  
Real Data ◽  
Rate Function ◽  
The Other ◽  
Likelihood Method ◽  
Model Parameters ◽  
Data Sets ◽  
Gompertz Distribution ◽  
Probability And Statistics ◽  
Analytical Behavior

Unit distributions are commonly used in probability and statistics to describe useful quantities with values between 0 and 1, such as proportions, probabilities, and percentages. Some unit distributions are defined in a natural analytical manner, and the others are derived through the transformation of an existing distribution defined in a greater domain. In this article, we introduce the unit gamma/Gompertz distribution, founded on the inverse-exponential scheme and the gamma/Gompertz distribution. The gamma/Gompertz distribution is known to be a very flexible three-parameter lifetime distribution, and we aim to transpose this flexibility to the unit interval. First, we check this aspect with the analytical behavior of the primary functions. It is shown that the probability density function can be increasing, decreasing, “increasing-decreasing” and “decreasing-increasing”, with pliant asymmetric properties. On the other hand, the hazard rate function has monotonically increasing, decreasing, or constant shapes. We complete the theoretical part with some propositions on stochastic ordering, moments, quantiles, and the reliability coefficient. Practically, to estimate the model parameters from unit data, the maximum likelihood method is used. We present some simulation results to evaluate this method. Two applications using real data sets, one on trade shares and the other on flood levels, demonstrate the importance of the new model when compared to other unit models.

Small specimen techniques for estimation of tensile, fatigue, fracture and crack propagation material model parameters

2021 ◽  
pp. 030932472110252
Author(s):  
Julija Kazakeviciute ◽  
James Paul Rouse ◽  
Davide Focatiis ◽  
Christopher Hyde
Keyword(s):  
Fatigue Fracture ◽  
Structural Integrity ◽  
Standard Specimen ◽  
Creep Behaviour ◽  
Parameter Determination ◽  
Model Parameters ◽  
Small Specimen ◽  
Testing Methods ◽  
Advantages And Disadvantages ◽  
Tensile Fatigue

Small specimen mechanical testing is an exciting and rapidly developing field in which fundamental deformation behaviours can be observed from experiments performed on comparatively small amounts of material. These methods are particularly useful when there is limited source material to facilitate a sufficient number of standard specimen tests, if any at all. Such situations include the development of new materials or when performing routine maintenance/inspection studies of in-service components, requiring that material conditions are updated with service exposure. The potentially more challenging loading conditions and complex stress states experienced by small specimens, in comparison with standard specimen geometries, has led to a tendency for these methods to be used in ranking studies rather than for fundamental material parameter determination. Classifying a specimen as ‘small’ can be subjective, and in the present work the focus is to review testing methods that utilise specimens with characteristic dimensions of less than 50 mm. By doing this, observations made here will be relevant to industrial service monitoring problems, wherein small samples of material are extracted and tested from operational components in such a way that structural integrity is not compromised. Whilst recently the majority of small specimen test techniques development have focused on the determination of creep behaviour/properties as well as sub-size tensile testing, attention is given here to small specimen testing methods for determining specific tensile, fatigue, fracture and crack growth properties. These areas are currently underrepresented in published reviews. The suitability of specimens and methods is discussed here, along with associated advantages and disadvantages.

scholarly journals Bayesian Inference of Species Trees using Diffusion Models

2020 ◽  
Vol 70 (1) ◽  
pp. 145-161 ◽  
Author(s):  
Marnus Stoltz ◽  
Boris Baeumer ◽  
Remco Bouckaert ◽  
Colin Fox ◽  
Gordon Hiscott ◽  
...  
Keyword(s):  
Bayesian Inference ◽  
Numerical Algorithms ◽  
Diffusion Models ◽  
Model Parameters ◽  
Data Sets ◽  
Species Trees ◽  
Computationally Efficient ◽  
Data Set ◽  
Snp Data ◽  
Binary Markers

Abstract We describe a new and computationally efficient Bayesian methodology for inferring species trees and demographics from unlinked binary markers. Likelihood calculations are carried out using diffusion models of allele frequency dynamics combined with novel numerical algorithms. The diffusion approach allows for analysis of data sets containing hundreds or thousands of individuals. The method, which we call Snapper, has been implemented as part of the BEAST2 package. We conducted simulation experiments to assess numerical error, computational requirements, and accuracy recovering known model parameters. A reanalysis of soybean SNP data demonstrates that the models implemented in Snapp and Snapper can be difficult to distinguish in practice, a characteristic which we tested with further simulations. We demonstrate the scale of analysis possible using a SNP data set sampled from 399 fresh water turtles in 41 populations. [Bayesian inference; diffusion models; multi-species coalescent; SNP data; species trees; spectral methods.]

Language and identity in East Timor

2008 ◽  
Vol 32 (2) ◽  
pp. 153-180 ◽  
Author(s):  
Kerry Taylor-Leech
Keyword(s):  
Language Policy ◽  
Policy Development ◽  
East Timor ◽  
Language And Identity ◽  
Data Sets ◽  
Structured Interviews ◽  
Student Focus ◽  
Research Findings ◽  
Official Languages

Language choice in the newly independent Republic of East Timor can be usefully examined in the wider context of language policy in multilingual states. The present article reports on ethnographic research investigating official and popular discourses of language and identity in East Timor and the role of past and present language policies and practices in shaping national and social identity. It focuses on the discursive reconstruction of identity through five official instruments of language policy development. Hostile discourses in the Australian and Indonesian press towards the choice of Portuguese (the former colonial language) and Tetum (the endogenous lingua franca) as official languages provided the context for the investigation. A persistent theme in these discourses is that English and/or Indonesian would be preferable choices. The article puts these discourses into perspective by presenting findings from two data sets: (i) the 2004 National Census and (ii) analysis of the discourses of 78 participants in semi-structured interviews and student focus groups. The census shows clear signs of the revival of Portuguese and the reinvigoration of Tetum. It also shows how diverse linguistic identities have become in East Timor. The research findings show that there is less hostility to official language policy than claimed in the Australian and Indonesian press. However, the findings also emphasise the urgent need to reconstruct an inclusive, plurilingual national identity that can encompass diversity.

scholarly journals A LOW-BIAS SIMULATION SCHEME FOR THE SABR STOCHASTIC VOLATILITY MODEL

2012 ◽  
Vol 15 (02) ◽  
pp. 1250016 ◽  
Author(s):  
BIN CHEN ◽  
CORNELIS W. OOSTERLEE ◽  
HANS VAN DER WEIDE
Keyword(s):  
Stochastic Volatility ◽  
Asset Price ◽  
Realistic Model ◽  
Stochastic Volatility Model ◽  
Model Parameters ◽  
Fixed Income ◽  
Financial Industry ◽  
Volatility Model ◽  
Discretization Schemes ◽  
Simulation Scheme

The Stochastic Alpha Beta Rho Stochastic Volatility (SABR-SV) model is widely used in the financial industry for the pricing of fixed income instruments. In this paper we develop a low-bias simulation scheme for the SABR-SV model, which deals efficiently with (undesired) possible negative values in the asset price process, the martingale property of the discrete scheme and the discretization bias of commonly used Euler discretization schemes. The proposed algorithm is based the analytic properties of the governing distribution. Experiments with realistic model parameters show that this scheme is robust for interest rate valuation.

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